High tension electrical apparatus



l.. EMANUELI HIGH TENSION ELECTRICAL APPARATUS Filed De. 26. 1935Attorneg.

Erwan uel Inventor June 28, 1938.

Patented June v28, 14.938

UNITED STATES PATENT ori-ICE Luigi Emanueli, Milan, Italy, assignor toSociet Italiana Pirelli, a corporation of Italy Application December 26,1935, Serial No. 56,282

In Italy January 30, 1935 3 Claims.

The present invention refers to high tension 'electrical apparatus andparticularly to terminals of electric cables, to bushings and to jointsof electric cables. It refers in general to all kinds 5 of apparatus inwhich there is a symmetrical distribution ofthe electric eld around anaxis and high gradients of potential near the electrodes.

The present invention has for its object the provision of an improvedform of electrode having an insulating covering of high dielectricstrength for controlling the distribution of the electric field in hightension electrical apparatus.

The attached drawing serves to illustrate the invention, wherein Figs.1, 2, 3 and 4 represent l5 various constructive forms of the insulatedelectrodes which embody the present invention; Fig. 5 shows a particularconstructive form of the electrical connection of the electrode, andFigs. 6, 7 and 8 show schematically electrical apparatus in whichelectrodes according to the present invention are used.

The type of electrode involving the subject matter of the presentinvention always has the toroidal form, that is, the form of a ring.Fig. l

where l-l indicates the symmetry axis of the electric field, 2 theelectrode made of conductive material, either solid, as drawn, orhollow, or even filled with another material. It has a covering 3 ofinsulating material in the form of a tape wound thereon with tight andoverlapping spirals which follow the outline of the meridian section ofthe ring, said tape being threaded through the central opening in thering and over the outer surface thereof to form layers. Thecross-section of the electrode can, according to the particular case, beeither round, elliptic, oval or of any other form, or even withrectilinear or concave portions. In all cases, the surfaces are wellrounded.

The insulation can be of various kinds, for example, of textilematerials, in particular silk. The most suitable material seems to bepaper, in the form of tape, preferably impregnated with i 45. insulatingfluid beforev or after its application lon the ring.

Owing to the different lengths of the parallel circles on the ring atthe various distances from the axis l-I, the insulation thickness willbe greater at the inner zone 5 nearer the axis and less at the outerzone 4.

In order to obtain a very compact winding without wrinkles in the paper,it is, of course, necessary that the width of the tape be proportionateboth to the minimum radius of the ring shows it in axial section in itsmost simple form, y

' surface slightly concave as shown in Fig. 2; in 5 such a case, whenthe tape has been wound, a band 6 of insulating material is applied veryI tightly on the winding along the parallel circles of the ring, on theconcave part of the surface, so that the covering comes at each point incon- 10 tact with the electrode. If this is done carefully, the windingwhen finished is always as compact as if it had been made on acylindrical electrode.

In the case of Fig. 3, electric tension is applied 15 between thetoroidal electrode 2a and an internal coaxial electrode or conductor l.In this case, the effective insulation is that on the internal portionof the surface of the ring. In the case of Fig. 4 instead, where theelectric tension is 20 applied between the toroidal electrode 2lD and anexternal coaxial electrode 1b, the elective insulation is that on theoutside part of the ring. In other ca ses, where the electric stress hasthe same direction as the axis, the effective parts are 25 one or bothof the end zones of the electrode which are perpendicular to the axis.The parts of the insulation which do no work need not necessarily becompressed very thoroughly or have a support. The toroidal electrode,there- 30 fore, when necessary for lightness or for other reasons, canbe made of sheet metal and have as its meridian section an opening, asshown in Figs. 3 and 4. In Fig. 3 the opening in the hollow electrode2EL faces outwardly while in Fig. 4 the 35 opening in the hollowelectrode 2b faces inwardly.

In a few cases, the electrode may be destined to work iloating, that iswithoutapplied potential but at a potential automatically determinedfrom the position of the electrode itself in the electric 40 field.

In most cases, however, the electrode will have to be electricallyconnected to parts of the circuit and will therefore be provided withconnecting means, which can be of various types and 45 which in eachcase will be called a connector. The connector will always be located ina place wherel the electric stress is weak or nil. In case the electrodeis hollow and has an incomplete surface, the connector will preferablybe located inside the electrode, as indicated at 8 in Figs. 3 and 4, anda small metallic wire or vstrand 9 will be connected here and passthrough a small hole made in the paper insulation on the side oppositeto the second electrode. The hole will, 55

of course, be made in the paper after it has been wound and the wire 9,previously provided inside the electrode, will be made to pass throughthe hole.

If the electrode is solid, the connector can be conveniently fixed tothe electrode itself, on a small fiat zone thereof as shown by A-A inFig. 5, fixing it after the insulation has been applied. In the zoneA--A, the insulation vwill not be as compact as in the rest of theelectrode. This fact, which will not have any dlsadvantageous electricaleiiect owing to the smallness of the zone. makes it possible toindividuate the zone itself so that the insulating covering can be boredat this point and the connector 8B introduced and fixed in a screw holeI located in the center 0f the zone. This operation will be easier ifthe entrance to the hole VIll is conical.

Electrodes forming the subject matter of the present invention can'beemployed in numerous cases. Among them may be mentioned, as ofparticular importance, cable terminals, bushings and cable joints.

Fig. 6 shows schematically a cable terminal where a series of toroldalelectrodes II covered with insulation is used. They are electricallyconnected together by connectors 8b and with the lead sheath I2 of thecable and have a gradually increasing diameter and form a. kind offunnel-shaped prolongation of the lead sheath. Owing to their highdielectric strength, they offer a considerable resistance to perforationin the region where a high gradient of potential is present.

Fig. '7 shows schematically a bushing. The

conductor I3 at the point of passage there through besides being coveredwith insulation I4, is surrounded by two series of toroidal electrodesII. These have a gradually increasing diameter on both sides of thecenter and are electrically connected together by wires 8b and to earthby wire 8.

A particularly important case is that of cable joints for high tensions.As shown in Fig. 8, toroidal electrodes II can first of all be used inthis case also, as in terminals, to build up a prolongation of the leadsheath with a high dielectric strength. The torcidial electrodes can,however, be used in the joints with still greater advantage to increasethe perforation tension between the jolnting socket I5 of the conductorslia of the two cables and the joint casing I6 which is connected at itsends to the lead sheath. It is well known that in many cases said sockethas necessarily an irregular surface, for instance as in stop-:jointsfor oil-filled cables, the latter having longitudinal channels Ib filledwith oil. It is then advisable to surround the socket with a metallicscreen I1 having a smooth external surface and electrically connected tothe socket. 'Ilriere is, in fact, a lower gradient of potential on itssurface, besides this it is easier to protect the screen than thesocket, by means of insultition, from the discharges against the casingI6. This screen also can be built up by an insulated toroidal electrodeaccording to the present inj vention, as for example, of the form shownPig. 4.

Lastly, other or auxiliary toroidal electrodes suitably covered withinsulation have been found very useful in joints, placing them near thetwo ends of the screen as shown in I8 of Fig. 8. These electrodes alsoare connected to the socket and are therefore put under tension. Theirfunction is to increase the perforation tension in the'regions near thetwo ends of the socket I5, which are particularly subject to discharge.

The insulated electrodes which are the object of the present inventioncan be used with advantage in other cases also, besides those mentionedabove, and it is understood that the construetive forms describedherein, of both the electrode and its connector, are only example cases.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electrode unit complete in itself for application as such to hightension electrical apparatus comprising a metal toroidal element havinga well rounded surface free of projections with a concave portion in theregion farthest from the axis thereof, impregnated insulating tapethreaded through the center of the element and over the entire roundedsurface thereof in layers and forming a complete covering therefor, anda binding band surrounding the element and holding the tape in contactwith the surface of said concave portion.

L 2. In combination, a pair olv1 sheathed high potential conductorsarranged end to end, each having a central core, a filling of liquidinsulation for the cores, insulation on the conductors which isimpregnated by the liquid insulation, a socket electrically uniting saidends, a main hollow toroidal electrode enclosing the socket andextending axially on both sides thereof and in which the socket iscentrally located, a pair of auxiliary electrodes of ring form ofshorter axial lengththan the main electrode located one closely adjacenteach end thereof where electrical stresses tend to be the greatest,connectors for electrically connecting the main and auxillary electrodesto the conductors so that they all have the same potential, andinsulation applied over the ends of the conductors and also over themain and auxiliary electrodes forming a covering therefor.

3. An electrode unit complete in itself for application as such to hightension electrical apparatus comprising a unitary ring having smoothinner and outer surfaces and well rounded ends and a small fiat zonelocated in a region where the electrical stress is less than themaximum, insulating tape tightly wound in overlapping layers over thesurface of the ring to form a complete covering therefor, said tapeextending axially over the inner and outer surfaces and over the roundedends, the covering having a perforation located at said flat zone, and aconnector extending through the perforation into the ring forestablishing an electrical connection between the ring and a conductorexternal thereto.

LUIGI EMANUELI.

